BANGKOK, Thailand — Somchai Wongsawat was nominated by the ruling party’s executive board yesterday to become Thailand’s next prime minister, making him the most likely to assume the post in a parliamentary vote tomorrow.

The People Power Party’s executive board will nominate Mr. Somchai once the choice is ratified by party legislators, a spokesman, Kudeb Saikrajang, told reporters yesterday. The House of Representatives, where the PPP-led coalition holds 315 of 480 seats, is scheduled to elect a successor to Samak Sundaravej on September 17.

Mr. Somchai, a relative of former Prime Minister Thaksin Shinawatra, will probably only last a few months if he takes office, the secretary-general of the PPP, Surapong Suebwonglee, said in an interview yesterday in Bangkok. More than 10,000 protesters who have occupied the prime minister’s ceremonial office complex for almost three weeks say they will oppose anyone from the party.

“There won’t likely be an immediate house dissolution but I am not sure how long this new government will last,” Nr, Surapong, who’s also Thailand’s finance minister, said. “Most of the political observers think the new government may not last longer than a couple of months.”